Location: Mitchelstown, Co. Cork, Ireland • Sector: Food & Beverage

The Client:
Dairygold Co-Operative Society Limited is Ireland’s largest farmer-owned dairy business and the country’s second largest dairy processor. The co-operative’s wide range of products include whole, skim, and buttermilk powders; milk proteins; butter (salted, unsalted, and lactic); cheese and cheese powders; and a variety of whey products. Dairygold’s success has been built through 100 years of co-op heritage and dairy processing excellence.

The Client’s Needs:
Headquartered in Mitchelstown, Co. Cork, Ireland, Dairygold’s production facility converts approximately 960 million liters (254 million gallons) of milk annually into top quality dairy products. Dairygold needed a wastewater treatment system that could reliably treat process wastewater containing powdered milk and cheese waste, as well as high-strength salty whey.

Due to periodic overloading of Dairygold’s pre-existing biological nutrient removal (BNR) plant, foul odor had also become a concern of the surrounding community. Dairygold was keen to be a good neighbor and was committed to finding a solution.

The Solution:
ADI Systems designed an anaerobic digestion system and supplied and installed its proprietary technology package at Dairygold’s facility in Mitchelstown. The system is comprised of an above-ground 45,000 m3 (12 MG) proprietary low-rate anaerobic ADI-BVF® reactor. The Type S BVF® digester is designed to pretreat a large portion of the process wastewater from Dairygold’s production facility prior to it entering the BNR system. The remaining process wastewater is bypassed to provide a carbon source for the BNR.

At design conditions, the BVF® reactor anaerobically digests the majority of the organic load; it converts the degradable organics in the wastewater into energy-rich biogas and generates a small amount of waste anaerobic sludge (WANS). The reactor releases a high-quality anaerobic effluent to feed the existing downstream BNR system.

Two heat exchangers are used to capture heat from the effluent and transfer it to the influent before it enters the BVF® reactor.

The Results:
The BVF® reactor has proven to be a simple, efficient, low-maintenance method of treating dairy processing wastewater. The BVF® system also provides satisfactory performance at lower than optimal temperatures. Treatment is reliable, robust, and resilient against shock hydraulic and organic loadings.

The characteristics of the combined wastewater and anaerobic BVF® reactor effluent, measured over a 1.5-year period, are summarized below.

Parameter

Design Characteristics

Combined Raw Wastewater

BVF® Reactor Effluent

Flow* (m3/d)

7,500

5,500

5,500

COD (mg/l)

2,900

2,850

200

BOD (mg/l)

1,920

1,560

40

TSS (mg/l)

800

700

160

pH

4.0-11.0

1.7-12.9

6.5-7.9

Temperature

28-30oC (82-86oF)

-

29oC (84oF)

*at full-load operations

Thanks to Dairygold’s new anaerobic digester (ADI-BVF® reactor), the dairy can be confident its process wastewater meets strict discharge limits.

The BVF® reactor is completely covered with a floating geomembrane cover, which collects biogas produced during the anaerobic digestion process and prevents the release of foul odors. This, in combination with anaerobic pretreatment, has eliminated odor issues, thereby improving the company’s reputation in the town of Mitchelstown.

As part of Dairygold’s efforts for continued sustainability, the biogas is converted into renewable energy. A portion of the biogas is used in a dual-fuel boiler to produce hot water to heat the BVF® reactor. The remaining portion of the biogas is used for supplementing heating requirements in a plant boiler or burned in a waste gas flare.